Summary:
When expiration is set in a pessimistic transaction, `txn_state_` is already updated to `AWAITING_PREPARE` in the `if (expiration_time_ > 0)` block, there is no need to update the state in `if (can_prepare)` block again.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6778
Test Plan: make check
Reviewed By: lth
Differential Revision: D21335319
Pulled By: cheng-chang
fbshipit-source-id: 251d634cc7d1a0e86e673a59f0bda8584da5a35f
Summary:
In current commit protocol of pessimistic transaction, if the transaction is not prepared before commit, the commit protocol implicitly assumes that the user wants to commit without prepare.
This PR adds TransactionOptions::skip_prepare, the default value is `true` because if set to `false`, all existing users who commit without prepare need to update their code to set skip_prepare to true. Although this does not force the user to explicitly express their intention of skip_prepare, it at least lets the user be aware of the assumption of being able to commit without prepare.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6775
Test Plan: added a new unit test TransactionTest::CommitWithoutPrepare
Reviewed By: lth
Differential Revision: D21313270
Pulled By: cheng-chang
fbshipit-source-id: 3d95b7c9b2d6cdddc09bdd66c561bc4fae8c3251
Summary:
The dynamic_cast in the filter benchmark causes release mode to fail due to
no-rtti. Replace with static_cast_with_check.
Signed-off-by: Derrick Pallas <derrick@pallas.us>
Addition by peterd: Remove unnecessary 2nd template arg on all static_cast_with_check
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6732
Reviewed By: ltamasi
Differential Revision: D21304260
Pulled By: pdillinger
fbshipit-source-id: 6e8eb437c4ca5a16dbbfa4053d67c4ad55f1608c
Summary:
Based on https://github.com/facebook/rocksdb/issues/6648 (CLA Signed), but heavily modified / extended:
* Implicit capture of this via [=] deprecated in C++20, and [=,this] not standard before C++20 -> now using explicit capture lists
* Implicit copy operator deprecated in gcc 9 -> add explicit '= default' definition
* std::random_shuffle deprecated in C++17 and removed in C++20 -> migrated to a replacement in RocksDB random.h API
* Add the ability to build with different std version though -DCMAKE_CXX_STANDARD=11/14/17/20 on the cmake command line
* Minimal rebuild flag of MSVC is deprecated and is forbidden with /std:c++latest (C++20)
* Added MSVC 2019 C++11 & MSVC 2019 C++20 in AppVeyor
* Added GCC 9 C++11 & GCC9 C++20 in Travis
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6697
Test Plan: make check and CI
Reviewed By: cheng-chang
Differential Revision: D21020318
Pulled By: pdillinger
fbshipit-source-id: 12311be5dbd8675a0e2c817f7ec50fa11c18ab91
Summary:
Although there are tests related to locking in transaction_test, this new test directly tests against TransactionLockMgr.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6599
Test Plan: make transaction_lock_mgr_test && ./transaction_lock_mgr_test
Reviewed By: lth
Differential Revision: D20673749
Pulled By: cheng-chang
fbshipit-source-id: 1fa4a13218e68d785f5a99924556751a8c5c0f31
Summary:
1. If expiration_time is non-positive, no need to call NowMicros, save a syscall.
2. expire_time should only be set when expired is false.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6586
Test Plan: make check
Reviewed By: lth
Differential Revision: D20673730
Pulled By: cheng-chang
fbshipit-source-id: a69e8d7b16dc6d0d00487bb1c19f0710d79482e2
Summary:
The last key may hit index of out bound exception when id = 9.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6574
Reviewed By: riversand963
Differential Revision: D20699791
Pulled By: cheng-chang
fbshipit-source-id: 8e2c5be5ff0e53e9857cfd59cea97cff21446819
Summary:
In most places in the code the variable names are spelled correctly as
COMMITTED but in a couple places not. This fixes them and ensures the
variable is always called COMMITTED everywhere.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6481
Differential Revision: D20306776
Pulled By: pdillinger
fbshipit-source-id: b6c1bfe41db559b4bc6955c530934460c07f7022
Summary:
Today `WriteUnpreparedTxn::RollbackInternal` will write the rollback batch assuming that there is only a single subbatch. However, because untracked_keys_ are currently not deduplicated, it's possible for duplicate keys to exist, and thus split the batch. Also, tracked_keys_ also does not support compators outside of the bytewise comparators, so it's possible for duplicates to occur there as well.
To solve this, just pass in the correct subbatch count.
Also, removed `WriteUnpreparedRollbackPreReleaseCallback` to unify the Commit/Rollback codepaths some more.
Also, fixed a bug in `CommitInternal` where if 1. two_write_queue is true and 2. include_data is true, then `WriteUnpreparedCommitEntryPreReleaseCallback` ends up calling `AddCommitted` on the commit time write batch a second time on the second write. To fix, `WriteUnpreparedCommitEntryPreReleaseCallback` is re-initialized.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6463
Differential Revision: D20150153
Pulled By: lth
fbshipit-source-id: df0b42d39406c75af73df995aa1138f0db539cd1
Summary:
When dynamically linking two binaries together, different builds of RocksDB from two sources might cause errors. To provide a tool for user to solve the problem, the RocksDB namespace is changed to a flag which can be overridden in build time.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6433
Test Plan: Build release, all and jtest. Try to build with ROCKSDB_NAMESPACE with another flag.
Differential Revision: D19977691
fbshipit-source-id: aa7f2d0972e1c31d75339ac48478f34f6cfcfb3e
Summary:
For write unprepared, some applications may bypass the transaction api, and write keys directly into the write batch. However, since they are not tracked, rollbacks (both for savepoint and transaction) are not aware that these keys have to be rolled back.
The fix is to track them in `WriteUnpreparedTxn::untracked_keys_`. This is populated whenever we flush unprepared batches into the DB.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6404
Differential Revision: D19842023
Pulled By: lth
fbshipit-source-id: a9edfc643d5c905fc89da9a9a9094d30c9b70108
Summary:
I create a new branch from the branch new upsteram/master and "git merge --squash".
Maybe it will fix everything.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6420
Differential Revision: D19897152
Pulled By: zhichao-cao
fbshipit-source-id: 6575d9e3b23e360f42ee1480b43028b5fcc20136
Summary:
Unfortunately, it seems like mysqld reuses xids across machine restarts. When that happens, we could have something like the following happening:
```
BEGIN_PREPARE(unprepared) Put(a) END_PREPARE(xid = 1)
-- crash and recover with Put(a) rolled back as it was not prepared
BEGIN_PREPARE(prepared) Put(b) END_PREPARE(xid = 1)
COMMIT(xid = 1)
-- crash and recover with both a, b
```
To solve this, we will have to log the rollback batch into the WAL during recovery.
WritePrepared already logs the rollback batch into the WAL, if a rollback happens after prepare, so there is no problem there.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6418
Differential Revision: D19896151
Pulled By: lth
fbshipit-source-id: 2ff65ddc5fe75efd57736fed4b7cd7a109d26609
Summary:
A recent fix related to 2pc https://github.com/facebook/rocksdb/pull/6313/ writes something to WAL, but does not flush or sync. This causes assertion failure "impl->TEST_WALBufferIsEmpty()" if manual_wal_flush = true. We should fsync the entry to make sure a second power reset can recover.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6417
Test Plan: Add manual_wal_flush=true case in TransactionTest.DoubleCrashInRecovery and fix a bug in the test so that the bug can be reproduced. It passes with the fix.
Differential Revision: D19894537
fbshipit-source-id: f1e84e49e2269f583c6019743118292cd8b6598e
Summary:
Unit test names, together with other components, are used to create log files
during some internal testing. Overly long names cause infra failure due to file
names being too long.
Look for internal tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6352
Differential Revision: D19649307
Pulled By: riversand963
fbshipit-source-id: 6f29de096e33c0eaa87d9c8702f810eda50059e7
Summary:
In WritePrepared there could be gap in sequence numbers. This breaks the trick we use in kPointInTimeRecovery which assume the first seq in the log right after the corrupted log is one larger than the last seq we read from the logs. To let this trick keep working, we add a dummy entry with the expected sequence to the first log right after recovery.
Also in WriteCommitted, if the log right after the corrupted log is empty, since it has no sequence number to let the sequential trick work, it is assumed as unexpected behavior. This is however expected to happen if we close the db after recovering from a corruption and before writing anything new to it. To remedy that, we apply the same technique by writing a dummy entry to the log that is created after the corrupted log.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6313
Differential Revision: D19458291
Pulled By: maysamyabandeh
fbshipit-source-id: 09bc49e574690085df45b034ca863ff315937e2d
Summary:
unordered_write is incompatible with non-zero max_successive_merges. Although we check this at runtime, we currently don't prevent the user from setting this combination in options. This has led to stress tests to fail with this combination is tried in ::SetOptions.
The patch fixes that and also reverts the changes performed by https://github.com/facebook/rocksdb/pull/6254, in which max_successive_merges was mistakenly declared incompatible with unordered_write.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6284
Differential Revision: D19356115
Pulled By: maysamyabandeh
fbshipit-source-id: f06dadec777622bd75f267361c022735cf8cecb6
Summary:
WritePreparedTxnDB calls CancelAllBackgroundWork in its destructor to avoid dangling references to it from background job's SnapshotChecker callback. However, if the DBImpl is already closed, the info log might be closed with it, which causes memory leak when CancelAllBackgroundWork tries to print to the info log. The patch fixes that by calling CancelAllBackgroundWork only if the db is not closed already.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6268
Differential Revision: D19303439
Pulled By: maysamyabandeh
fbshipit-source-id: 4228a6be7e78d43c90630347baa89b008200bd15
Summary:
This is a continuation of https://github.com/facebook/rocksdb/pull/5320/files
I open a new mr for these purposes, half a year has past since the old mr is posted so it's almost impossible to fulfill some points below on the old mr, especially 5)
1) add validation modes for optimistic txns
2) modify unittests to test both modes
3) make format
4) refine hash functor
5) push to master
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6240
Differential Revision: D19301296
fbshipit-source-id: 5b5b3cbd39558f43947f7d2dec6cd31a06386edb
Summary:
allow_concurrent_memtable_write is incompatible with non-zero max_successive_merges. Although we check this at runtime, we currently don't prevent the user from setting this combination in options. This has led to stress tests to fail with this combination is tried in ::SetOptions. The patch fixes that.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6254
Differential Revision: D19265819
Pulled By: maysamyabandeh
fbshipit-source-id: 47f2e2dc26fe0972c7152f4da15dadb9703f1179
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6192
Test Plan:
Add a unit test that fails without the fix and passes now
make check
Differential Revision: D19124781
Pulled By: anand1976
fbshipit-source-id: 8c8cb6fa16c3fc23ec011e168561a13f76bbd783
Summary:
**NOTE**: this also needs to be back-ported to 6.4.6 and possibly older branches if further releases from them is envisaged.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6081
Differential Revision: D18710107
Pulled By: zhichao-cao
fbshipit-source-id: 03260f9316566e2bfc12c7d702d6338bb7941e01
Summary:
SmallestUnCommittedSeq sometimes takes too long when run under Valgrind. The patch disables it when the tests are run under Valgrind.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6035
Differential Revision: D18509198
Pulled By: maysamyabandeh
fbshipit-source-id: 1191443b9fedb6b9c50d6b76f5c92371f5030230
Summary:
For MDEV-19670: MyRocks: key lookups into deleted data are very slow
BaseDeltaIterator remembers iterate_upper_bound and will not let delta_iterator_
walk above the iterate_upper_bound if base_iterator_ is not valid
anymore.
== Rationale ==
The most straightforward way would be to make the delta_iterator
(which is a rocksdb::WBWIIterator) to support iterator bounds. But
checking for bounds has an extra CPU overhead.
So we put the check into BaseDeltaIterator, and only make it when
base_iterator_ is not valid.
(note: We could take it even further, and move the check a few lines
down, and only check iterator bounds ourselves if base_iterator_ is
not valid AND delta_iterator_ hit a tombstone).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5403
Differential Revision: D15863092
Pulled By: maysamyabandeh
fbshipit-source-id: 8da458e7b9af95ff49356666f69664b4a6ccf49b
Summary:
MaxCatchupWithNewSnapshot tests that the snapshot sequence number will be larger than the max sequence number when the snapshot was taken. However since the test does not have access to the max sequence number when the snapshot was taken, it uses max sequence number after that, which could have advanced the snapshot by then, thus making the test flaky.
The fix is to compare with max sequence number before the snapshot was taken, which is a lower bound for the value when the snapshot was taken.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5850
Test Plan: ~/gtest-parallel/gtest-parallel --repeat=12800 ./write_prepared_transaction_test --gtest_filter="*MaxCatchupWithNewSnapshot*"
Differential Revision: D17608926
Pulled By: maysamyabandeh
fbshipit-source-id: b122ae5a27f982b290bd60da852e28d3c5eb0136
Summary:
- Updated our included xxhash implementation to version 0.7.2 (== the latest dev version as of 2019-10-09).
- Using XXH_NAMESPACE (like other fb projects) to avoid potential name collisions.
- Added fastrange64, and unit tests for it and fastrange32. These are faster alternatives to hash % range.
- Use preview version of XXH3 instead of MurmurHash64A for NPHash64
-- Had to update cache_test to increase probability of passing for any given hash function.
- Use fastrange64 instead of % with uses of NPHash64
-- Had to fix WritePreparedTransactionTest.CommitOfDelayedPrepared to avoid deadlock apparently caused by new hash collision.
- Set default seed for NPHash64 because specifying a seed rarely makes sense for it.
- Removed unnecessary include xxhash.h in a popular .h file
- Rename preview version of XXH3 to XXH3p for clarity and to ease backward compatibility in case final version of XXH3 is integrated.
Relying on existing unit tests for NPHash64-related changes. Each new implementation of fastrange64 passed unit tests when manipulating my local build to select it. I haven't done any integration performance tests, but I consider the improved performance of the pieces being swapped in to be well established.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5909
Differential Revision: D18125196
Pulled By: pdillinger
fbshipit-source-id: f6bf83d49d20cbb2549926adf454fd035f0ecc0d
Summary:
This PR eliminates repeated lookups in associative or ordered containers when a single lookup suffices.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5875
Differential Revision: D17753172
Pulled By: anand1976
fbshipit-source-id: 796b02b760082521d8c42a1cb65a76bf0e6c1b8e
Summary:
Further apply formatter to more recent commits.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5830
Test Plan: Run all existing tests.
Differential Revision: D17488031
fbshipit-source-id: 137458fd94d56dd271b8b40c522b03036943a2ab
Summary:
Some recent commits might not have passed through the formatter. I formatted recent 45 commits. The script hangs for more commits so I stopped there.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5827
Test Plan: Run all existing tests.
Differential Revision: D17483727
fbshipit-source-id: af23113ee63015d8a43d89a3bc2c1056189afe8f
Summary:
Move definition and implementation for ArenaWrappedDBIter into its own .h/.cc files. Also, change inlining of functions to better comply with the Google C++ style guide.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5801
Test Plan: make check
Differential Revision: D17371012
Pulled By: anand1976
fbshipit-source-id: c1361abc2851575111e357a63d88be3b3d6cb341
Summary:
Use delete to disable automatic generated methods instead of private, and put the constructor together for more clear.This modification cause the unused field warning, so add unused attribute to disable this warning.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5009
Differential Revision: D17288733
fbshipit-source-id: 8a767ce096f185f1db01bd28fc88fef1cdd921f3
Summary:
ReadYourOwnWriteStress occasionally times out on some platforms. The patch splits it to three.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5776
Differential Revision: D17231743
Pulled By: maysamyabandeh
fbshipit-source-id: d42eeaf22f61a48d50f9c404d98b1081ae8dac94
Summary:
This avoids rehashing the key in TrackKey() in case the key is not already
in the map of tracked keys, which will happen at least once per key used in a
transaction.
Additionally fix two typos.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5696
Differential Revision: D17210178
Pulled By: lth
fbshipit-source-id: 7e2c28e9e505c1d1c1535d435250cf2b191a6fdf
Summary:
Iterators reseek to the target key after iterating over max_sequential_skip_in_iterations invalid values. The logic is susceptible to an infinite loop bug, which has been present with WritePrepared Transactions up until 6.2 release. Although the bug is not present on master, the patch adds a unit test to prevent it from resurfacing again.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5727
Differential Revision: D16952759
Pulled By: maysamyabandeh
fbshipit-source-id: d0d973dddc8dfabd5a794931232aa4c862c74f51
Summary:
MyRocks currently sets `max_write_buffer_number_to_maintain` in order to maintain enough history for transaction conflict checking. The effectiveness of this approach depends on the size of memtables. When memtables are small, it may not keep enough history; when memtables are large, this may consume too much memory.
We are proposing a new way to configure memtable list history: by limiting the memory usage of immutable memtables. The new option is `max_write_buffer_size_to_maintain` and it will take precedence over the old `max_write_buffer_number_to_maintain` if they are both set to non-zero values. The new option accounts for the total memory usage of flushed immutable memtables and mutable memtable. When the total usage exceeds the limit, RocksDB may start dropping immutable memtables (which is also called trimming history), starting from the oldest one.
The semantics of the old option actually works both as an upper bound and lower bound. History trimming will start if number of immutable memtables exceeds the limit, but it will never go below (limit-1) due to history trimming.
In order the mimic the behavior with the new option, history trimming will stop if dropping the next immutable memtable causes the total memory usage go below the size limit. For example, assuming the size limit is set to 64MB, and there are 3 immutable memtables with sizes of 20, 30, 30. Although the total memory usage is 80MB > 64MB, dropping the oldest memtable will reduce the memory usage to 60MB < 64MB, so in this case no memtable will be dropped.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5022
Differential Revision: D14394062
Pulled By: miasantreble
fbshipit-source-id: 60457a509c6af89d0993f988c9b5c2aa9e45f5c5
Summary:
In valgrind_test, TransactionTest.GetWithoutSnapshot ran 2 hours and still didn't finish. Black list from valgrind_test to prevent timeout.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5715
Test Plan: run "make valgrind_test" and see whether the test is still generated.
Differential Revision: D16866009
fbshipit-source-id: 92c78049b0bc1c2b9a0dfc1b7c8a9206b36f02f0
Summary:
Fix a bug in write unprepared savepoints. When flushing the write batch according to savepoint boundaries, we were forgetting to flush the last write batch after the last savepoint, meaning that some data was not written to DB.
Also, add a small optimization where we avoid flushing empty batches.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5703
Differential Revision: D16811996
Pulled By: lth
fbshipit-source-id: 600c7e0e520ad7a8fad32d77e11d932453e68e3f
Summary:
In MyRocks, there are cases where we write while iterating through keys. This currently breaks WBWIIterator, because if a write batch flushes during iteration, the delta iterator would point to invalid memory.
For now, fix by disallowing flush if there are active iterators. In the future, we will loop through all the iterators on a transaction, and refresh the iterators when a write batch is flushed.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5699
Differential Revision: D16794157
Pulled By: lth
fbshipit-source-id: 5d5bf70688bd68fe58e8a766475ae88fd1be3190
Summary:
Fix the following clang analyze failures:
```
In file included from utilities/transactions/transaction_test.cc:8:
./utilities/transactions/transaction_test.h:174:14: warning: Attempt to delete released memory
delete root_db;
^
```
The destructor of StackableDB already deletes the root db and there is no need to delete the db separately.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5700
Test Plan: USE_CLANG=1 TEST_TMPDIR=/dev/shm/rocksdb OPT=-g make -j24 analyze
Differential Revision: D16800579
Pulled By: maysamyabandeh
fbshipit-source-id: 64c2d70f23e07e6a15242add97c744902ea33be5
Summary:
Currently, if a write is done without a snapshot, then `largest_validated_seq_` is set to `kMaxSequenceNumber`. This is too aggressive, because an iterator with a snapshot created after this write should be valid.
Set `largest_validated_seq_` to `GetLastPublishedSequence` instead. The variable means that no keys in the current tracked key set has changed by other transactions since `largest_validated_seq_`.
Also, do some extra cleanup in Clear() for safety.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5697
Differential Revision: D16788613
Pulled By: lth
fbshipit-source-id: f2aa40b8b12e0c0cf9e38c940fecc8f1cc0d2385
Summary:
With changes made in https://github.com/facebook/rocksdb/pull/5664 we meant to pass snap_released parameter of ::IsInSnapshot from the read callbacks. Although the variable was defined, passing it to the callback in WritePreparedTxnReadCallback was missing, which is fixed in this PR.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5691
Differential Revision: D16767310
Pulled By: maysamyabandeh
fbshipit-source-id: 3bf53f5964a2756a66ceef7c8f6b3ac75f102f48
Summary:
The changes transaction_test to set `txn_db_options.default_write_batch_flush_threshold = 1` in order to give better test coverage for WriteUnprepared.
As part of the change, some tests had to be updated.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5658
Differential Revision: D16740468
Pulled By: lth
fbshipit-source-id: 3821eec20baf13917c8c1fab444332f75a509de9
Summary:
SmallestUnCommittedSeq reads two data structures, prepared_txns_ and delayed_prepared_. These two are updated in CheckPreparedAgainstMax when max_evicted_seq_ advances some prepared entires. To avoid the cost of acquiring a mutex, the read from them in SmallestUnCommittedSeq is not atomic. This creates a potential race condition.
The fix is to read the two data structures in the reverse order of their update. CheckPreparedAgainstMax copies the prepared entry to delayed_prepared_ before removing it from prepared_txns_ and SmallestUnCommittedSeq looks into prepared_txns_ before reading delayed_prepared_.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5683
Differential Revision: D16744699
Pulled By: maysamyabandeh
fbshipit-source-id: b1bdb134018beb0b9de58827f512662bea35cad0
Summary:
This is a new API added to db.h to allow for fetching all merge operands associated with a Key. The main motivation for this API is to support use cases where doing a full online merge is not necessary as it is performance sensitive. Example use-cases:
1. Update subset of columns and read subset of columns -
Imagine a SQL Table, a row is encoded as a K/V pair (as it is done in MyRocks). If there are many columns and users only updated one of them, we can use merge operator to reduce write amplification. While users only read one or two columns in the read query, this feature can avoid a full merging of the whole row, and save some CPU.
2. Updating very few attributes in a value which is a JSON-like document -
Updating one attribute can be done efficiently using merge operator, while reading back one attribute can be done more efficiently if we don't need to do a full merge.
----------------------------------------------------------------------------------------------------
API :
Status GetMergeOperands(
const ReadOptions& options, ColumnFamilyHandle* column_family,
const Slice& key, PinnableSlice* merge_operands,
GetMergeOperandsOptions* get_merge_operands_options,
int* number_of_operands)
Example usage :
int size = 100;
int number_of_operands = 0;
std::vector<PinnableSlice> values(size);
GetMergeOperandsOptions merge_operands_info;
db_->GetMergeOperands(ReadOptions(), db_->DefaultColumnFamily(), "k1", values.data(), merge_operands_info, &number_of_operands);
Description :
Returns all the merge operands corresponding to the key. If the number of merge operands in DB is greater than merge_operands_options.expected_max_number_of_operands no merge operands are returned and status is Incomplete. Merge operands returned are in the order of insertion.
merge_operands-> Points to an array of at-least merge_operands_options.expected_max_number_of_operands and the caller is responsible for allocating it. If the status returned is Incomplete then number_of_operands will contain the total number of merge operands found in DB for key.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5604
Test Plan:
Added unit test and perf test in db_bench that can be run using the command:
./db_bench -benchmarks=getmergeoperands --merge_operator=sortlist
Differential Revision: D16657366
Pulled By: vjnadimpalli
fbshipit-source-id: 0faadd752351745224ee12d4ae9ef3cb529951bf
Cheng Chang